These are progressively wound springs. The part where the wire is close together is weak while the part with the wire loops farther apart it stronger.

Yes, I want you to think of springs as stronger or weaker not softer or harder because their job is to hold things up not for you to rest your head upon.

A progressively wound spring starts out weak and gets stronger as you compress it. A straight rate spring gets stronger at the same rate as you compress it. A straight spring with a rate of 100 lbs will compress one inch when you place 100 lbs on it, two inches with 200 lbs and so on. A similar progressive spring will start with a rate of 75 lbs, when that’s used up the stronger rate of 150 lbs takes over.

This sounds nice and comfortable and it is if you are sitting on a coach. But you are riding a motorcycle with suspension that moves fast near the top of it’s travel and slow near the bottom. You want to spend most of your time near the top so the wheels can get out of the way of the bumps. A spring that gives up the best part of the travel as soon as you sit on the bike is not what we want.

What happens when you ride over a bump near the bottom of your travel. The suspension can’t move up fast enough so that end of the bike has to move side to side to make up for the extra distance it has to travel over the bump compared to the other wheel. This is what causes that “cheap wallow” in turns.

So unless you have a fiddle and play it well keep away from the Devil and his agent of despair the progressively wound spring.

If I have to do this, your fork caps are way too tight.  The top triple clamp bolt will squeeze the fork tube onto the cap.   You don’t need to make the cap tight.   Just tighten it a little more than what you can get with just your hand.

Back in the day Jim’s first task was to get a fork or shock to work. There is no point to great valving if the oil can find another way to go. These forks had that problem. Jim had told me how he solved the problem but this was my first chance to do it myself. I have his old notes. There are 4 things you need to do differently from other forks. Two of them are small simple things. One is big and the 4th is just crazy. I did them one at a time so I could see what each did. This meant taking the fork apart four times but good science is worth it.

The photo is of the forks ready to go home because I forgot to take a photo sooner.

Check out this two part seal head from a Sachs shock. Notice the cir-clips that go above and below the head. Also the seal is one piece, combining the shaft seal and body seal rather than just having a shaft seal and an O-ring. Did you see the shaft bushing? No? That’s because there is none. This is not the best shock I’ve worked on.

A normal seal head is one piece with an O-ring between itself and the body and a O-ring, X-ring or seal for the shaft as well as a shaft bushing. You push the seal head into the shock body, install the clip and let the pressure hold the seal head against the clip.

To take a shock apart you just release the gas, push the seal head down and remove the clip then pull. But how do you push the seal head in if there is a clip bellow it? They must really not want me to rebuild this shock.

I took it apart but I could not bring myself to do something that dumb to put it back together. I made a normal seal head with bushing and held it in place with just one clip.

I had another reason for replacing the seal head. The American branch of Sachs does not even know what a motorcycle is. The American branch of the seal company does not import that seal and “Sir we would need 6 to 8 weeks to get it from Germany and there is a large minimum order.”

After this the re-valve was easy. Not! The piston/valve stack is as bad as the seal head but Jim taught me well and I fixed that too.

If someone tells you Sachs shocks can’t be rebuilt or re-valved tell ‘em you know a guy. This one cost $420 with a spring. The next one will have to included the price of the seal head, about $30 more.

There was a snake in Wave.

Fischer’s don’t come with rear stand spools but they do come with mounts so I just needed to make some spools. The MRX is heaver than the SV’s it will race against so I want my spools to be light. Note the trimmed bolt head and the drilled out center saving 3 grams from the normal bolt on the right.

I recessed the bolts far into the spools so I could use shorter bolts and so the spool will protect the head of the bolt in a crash. It’s hard to remove bolts that are damaged.

Total weight is 38 grams for both. This is un-sprung weight so I want as little as possible. They look good too.

Do you guys remember Particle? She is the first of two Fischer MRX’s that I’m building for two clients. Particle won her first ever race and is now living in Napa, CA.

Meet Wave. Get it? Particle & Wave, you know like light? If you don’t know, look it up or move along. Fischer MRX #2. We had race body work molds made when we did Particle so the painted body work is waiting for Wave. Now to turn her into a race/track day bike. Check out my next post to see how I got this far…

Jessica teaches math.  Can you tell?  Yesterday was Pi day so this post is late.

Her bike was here for my fork mods, stronger springs and re-valving.  After 3 track days in 4 days she had this to say:

“Hello Ed,

Go ahead and reach over your shoulder and give yourself a pat on the back.  The rebuilt shock now sprung properly works like a dream.  Jaw dropping and truly awesome.  My GS went from baby buggy to guided missile. I put the bike through all its paces, drove it hard and fast and performance is truly enhanced.  Gone is the springy all over-the-place ride now replaced with a sharp, firm and decisive ride.  I now can break hard in the turns without the rear wheel moving sideways.  It’s now planted and the bike goes exactly where and when I want it to.  What I thought was too much clearance above ground causing a poor ride was all suspension.  The bike now steers with the hips, and follows my inside knee.  I can lean over confidently and find myself in a taller gear moving faster and still with plenty of comfort.  Job well done!  Many thanks.  I also like the color of the aftermarket spring. I am 100% satisfied.”

I rebuilt Martin’s BMW GS rear shock and gave it a stronger spring.  I think he’s happy.  I think I may have to turn From Baby Buggy to Guided Missile into a slogan.